The problem of securing highly accurate readings on outdoor weather instruments has been longstanding. The instruments must be placed in a fairly exposed outdoor position, yet by doing so, excessive exposure to the sun, wind and rain results in inaccurate readings. If the instruments are excessively shielded, inaccurate readings also result. If the instruments are placed in a housing, sufficient sun-shielding and adequate ambient flowing air circulation interiorly of the housing are essential.
With respect to rain gauges, there has been a persistent problem in securing accurate readings with exceedingly light amounts of rainfall such as with a mist-type rain. In prior rainfall gauges, excessive amounts of water droplets would adhere to the rainwater collecting funnel with the result that with a very light mist-type rain little if any rainwater would enter the measuring flask.